Airplane landing gear



Jan. 1s, 1949. R. w. ALLEN. 2,459,737

AIRPLANE LANDING GEAR Filed July 9., 1943 Q Sheets-Sheet l Ir l j Jan.18, 1949.

R. w. ALLEN AIRPLANE LANDING GEAR 6 Sheets-Sheet 2 Filed Jul` 9, 1943,QAYMQnv w. Auw

Jan. 18, 1949.

R. w. ALLEN AIRPLANE` LNbINe GEAR 6 Sheets-Sheet 3 Filed July 9, 1943 3won/wm PYAYMON-I) W. ALLEN l'll lll' R. W. ALLEN AIRPLANE LANDING G'ARJan. 18, 1949.

6 Sheets-Sheet 4 Filed July 9, 1943 RAYMOND w ALLH Jan. 18, 1949. R. w;ALLEN 2,459,737

AIRPLANE LANDING GEAR Filed July 9, 1943 6 Sheets-Sheet 5 www, I

Jan. 18. 1949. R, w, ALLEN 2,459,737

' AIRPLANE LANDING GEAR Fned Julyl-s, 194s. e sheets-sheet e m @28j-"MaQAYMonD w. ALLEN www Patented Jan. 18, 1949 AIRPLAN E LANDING GEARRaymond W. Allen, Akron, Ohio, assignor to The Firestone Tire & RubberCompany, Akron, Ohio, a corporation of Ohio Application July 9, 1943,Serial No. 494,107

s claims. (ci. sos-1o) l This invention relates to airplane landinggear, and more especially it relates to landing gear of the charactermentioned wherein endless .tracks of the so-called caterpillar type aresubstituted for the pneumatic tires commonly used with landing gear foraircraft.

Aircraft landing gear of the type having endl less tracks mounted uponpivoted and articulated supporting structures are old and well known inthis art, but those developed heretoforehave serious disadvantages andlimitations which the present invention remedies. The landing gear shownherein is highly emcient and is particularly advantageous for use with very heavy planes which land at high speeds. superior to priorconstructions in that it will permit a heavy, high speed plane to landand take off safely on very rough and uneven terrain. While earlierforms of landing gears have sought to achieve this result, the landinggear shown herein is more emcient and effective. It is also betteradapted for use on wet and muddy iields than other forms of landingdevices.

Other objects of the invention are to provide airplane landing gear ofthe caterpillar type capable of taking off and landing at higher speedsthan heretofore possible and to provide a structure of the charactermentioned capable of absorbing the higher impact forces resulting fromsuch higher speeds.

Another object of the invention is to provide for keeping the endlesstrack taut while the airplane is running on the ground either in landingor taxiing. Another object of the invention is to improve upon theconstruction of the track so as to better fit it for the servicerequired.

AMore specifically the landing gear of the in- -vention aims to providea bogie construction that will support a portion of the load; to providearticulated bogies 'so that the track willr follow the uneven contour ofthe ground;` to provide a exible support for the bogies to enableefiicient operation thereof; and to provide means compensating for thelengthening of the track due to tension when a heavy load is applied.Other objects will be manifest as the description proceeds.

Of the accompanying drawings:

Fig. 1 is a perspective View of a grounded airplane, and landing gearembodying the invention supporting the same;

Fig. 2 is a perspective view, on a larger scale, of landing gear such asshown in Fig. 1;

Fig. 3 is a section, on -a smaller scale, on the line 3 3 F18. 4;

It is also Fig. 4 is a side elevation of the track portion of thelanding gear, shown in full lines under load on a level surface;

Fig. 5 is a plan View of the structure shown in Fig. 4, a portionthereof being in section on line 5-5 of Fig. 4;

Fig. 6 is a side elevation of the landing gear in extended position itassumes when the plane is in the air and ready for landing;

Fig. 7 is a side elevation iof the structure shown in Fig, 6 as itappears under full load on a downwardly inclinded surface;

Fig. 8 is a side elevation of the structure shown in Figs. 6 and 7 as itappears when fully loaded and passing over an obstruction on the ground;

Fig. 9 is a side elevationpartly in section illustrating the retractedposition of the landing gear; and

Fig. 1G is a sectional detail of the endless band track.

Referring to Fig. 1 of the drawings, there is shown an airplane IIJ ofthe bomber type' comprising nacelles II,` II mounted upon the wingsthereof. Within the nacelles are the motors that drive the propellers I2of the airplane. Near its nose the airplane is provided with aretractible landing wheel I3, which Wheel is shown in opera'- tive orlowered position, the doors I4, I4 of its compartment being open. Thetail wheel of the craft is shown at I5. Within each nacelle II,rearwardly of the motor therein, is a compartment or bay within which ismounted a retractible landing gear that is designated as a unit by thecharacter A and which is an embodiment of the present invention. Thelanding units A are shown in the lowered or operative position theyassume when supporting the airplane upon the ground, the doors I6, whichclose the compartments of the landing units A when the latter are'inretracted or flying position, being shown open. Within each nacelle is'atriangular framework I'l, shown in broken lines in Figs. 6, 7 and 8, to`which a landing unit A is attached and which may represent a retractiblesupport. for the landing gear, but as said framework is no part of thepresent inventi'on, a more comprehensive showing thereof is notnecessary. Fig. 9 illustrates the landing units in retracted positionwithin nacelle II.

Pivotally connected at I9 to one corner of the triangular framework I1is an arm 20 and pivotally connected at 2l to another corner of theframework I1 'is a somewhat longer arm 22. The arms 20, 22 have theirlower ends plvotally connected at 23 and 24, respectively, to an arm 25that is obliquely disposed with relation to the horizontal with itsupper end disposed rearwardly. The pivotal connection 23 is at the upperend of arm 25 and the pivotal connection 24 is located intermediate theends of the arm,

but somewhat nearer the lower end. The arms4 20, 22 and 25 constitute aflexible strut or undercarriage structure that carries the track portionof the landing gear, and also carries a shock absorbing element thatabsorbs much of the shock incidental to landing of the airplane, andalso prevents rebound thereof. The shock absorbing element, shown at 26in the drawings, is of conventional telescoping type employing a heavyfluid in the manner of a dashpot, one end of said element beingplvotally connected to the arms 22 and 25 at the pivot point 24 and theother end of the element being pivotally connected to the arm 20 at 2l,intermediate the ends of the latter but somewhat near pivotal connectioni9. The arrangement is such that the arms 20, 22 and 25 assume therelative angular position best shown in Figs. 7 and 8 when theundercarriage is under load, as when the airplane is on the ground, andassume: the relative angular positions shown in Fig. 6 when the airplaneis oif the ground with landing gear in extended landing position, theshock absorbing element 26 being so positioned as yieldingly to opposesudden change in the relative positions of said arms.

'I'he track portion of the landing gear or the track unit comprises aframework or frame member consisting of parallel, spaced-apart,hollowside rails 30, 30 that are permanently connected to each otherintermediate their ends by a transverse brace or plate 3|. Between thebrace 3| and the rear ends of the side rails 30 the latter carry atransversely extending shaft 32 to which the lower end of the arm 25 ispivotally connected.

3l support the overbalanced weight of the track unit which wouldotherwise cause the track unit to drop into a vertical position. Thisdevice will permit the track unit to swing upwardly about' the pivot 32in riding over an obstruction. as shown in Fig. 8, and when the planelands. the load applied to the rear portion of the track will cause thetoggle formed by the lever 25 and vthe frame 30 to straighten out, thusbringing down the forward end of the track unit, the spring beingfurther compressed during this movement.

Fixedly mounted in the forward extremity of the side rails 30 andsupported at its ends thereby is a hollow axle 40, and journaledthereon, between said end rails, is a relatively large, hollow wheel ordrum 4|. Collars, such as the collar 42, Fig. 5, are mounted on the axle40 and retain the drum 4| centrally of the axle in spaced relation tothe side rails 30. The periphery of the drum is formed with a pluralityof circumferentially extendingv V-shaped grooves adapted frictionally toengage with complementally shaped ribs 43, 43, Figs. 5 and 10, formed onthe inner face of an endless band track or caterpillar element 44,constituting the ground-engaging member of the landing gear. Journaledon the axle 40 between the collars 42 and side rails 30 are arms 45,which arms extend obliquely downwardly and rearwardly and have theirlower or free ends connected by a hollow axle 46.- A relatively smallhollow wheel or drum"41 is journaled on the axle 45, the periphery ofthe drum being formed with circumferentially extending V-shaped groovesin which the ribs 43 of the endless track 44 are receivable. The freeends of the arms 45 normally are yieldingly urged rearwardly by tensionsprings 48, each ofwhich is connected at one end to a xed point on thecross-brace 3|, see Fig. 2, and

has its other end connected to a metal clip 49 40 secured upon aprojecting end portion of the axle As is best shown in Fig. 2, the arm25 is a trusslike structure having two lateral members 25a, 25a, thelower ends of the latter being spaced apart so as to connect with theshaft 32 at opposite end portions thereof, and being positioned besidethe inner lateral faces of the respective side rails 30. Preferably theshaft 32 is hollow to reduce weight. The track portion of the landinggear is arranged to be carried in determinate angular position withrelation to the arm 25 at times when there is no load on said trackportion. When the landing gear is extended preparatory to landing, thetrack portion will be somewhat oblique with relation to horizontal, itsleading end being elevated as compared to its trailing end. Thisposition of the track portion is shown in Fig. 6. For yieldingly holdingthe track portion to the angular position mentioned, the lateral members25a of arms 25 are provided, between pivot points 23, 24, withupstanding brackets 33 that support a hollow transverse bar or shaft 34.The latter projects from opposite sides of said arm 25, and to eachprojecting end portion thereof is swivelled the rear end of a cylinder35. In each cylinder 35 is a compression spring 36, Fig. 4, and a rod 31engaged with said spring and projecting from an apertured closure on.the front end of said cylinder. The outer end of each rod 31 isplvotally .connected to an anchor bracket 38 securedl to a side rail 30between the pivot point or shaft 32 and the forward end of the rail,which is the right end thereof as shown in Fig. 2 and the left endthereof as shown in Figs. 4 to 8. The structures consisting of thecylinders 35, springs 36 and rods 45, beside arm 45.

A hollow shaft 5| is iixedly mounted in the rearward extremity of theside rails 30, and journaled on ,said shaft between said side rails andadjacent the,latter are arms 52 which extend obliquely downwardly andrearwardly, substantially in parallelism with the arms 45, and havetheir lower, free ends connected by a hollow axle 53. Journaled upon theaxle 53 between arms 52 is a hollow wheel or drum 54 of substantiallythe same diameter as the drum 4| at the front end of the landing gear,the periphery of said drum being formed with V-shaped grooves in whichthe ribs 43. of the endless track 44 are receivable. As shown in Fig. 5,the drum 54 is provided interiorly at one end with a brake of theconventional uid pressure operated friction disc type. The hub and rimportion oi' the drum are con-y nected by an annular structure 55 thatcarries one set of brake-discs, the other set being carried by anannular fixture 55 that is bolted to a flange 51 formed on the arm 52.Pressure uid for actuating the brake is conducted to the latter by aflexible conduit 55 that connects with a suitable port formed in saidfixture 55. Obviously a similar brake could be provided at the other endof the drum, which brake would be connected in parallel with the fluidsupply conduit 58. When the landing gear is applied to aircraft carryingheavier loads, the forward drum 4| also may be equipped with brakingmeans.

Positioned between the drum 4l and the drum 54 is a bogie comprising adat top plate 30 and end plates 5|, 5| that are of trapezoidal shape,

the top plate being secured to the shorter of the parallelzsides of theend plates. The end plates Il carry two hollow axles 62, 82, and'journaled on said axles are hollow wheels or drums 63., The bogle wheels83 are identical with each other and preferably are identical with thedrum 41. The periphery ofeach wheel 53 is also formed with the V-shapedgrooves for the endless track 44.

Journaled in bearings in each .end plate 3l is a shaft 34; the ends oiwhich project laterally vbeyond said end plates. Pivotally connected toeach of the projecting end portions of shaft 64 are two links 65 and B6,which links extend forwardly and rearwardly. respectively, both of thelinks on either side of the structure vbeing disposedin the samevertical plane. The rear end of each oi the rearwardly extending links56 is pivotally connected to a projecting end portion of the rear axle53 of the structure, and the front ends of the links 65 are pivotallyconnected at a midway point to the arms 45 by the shaft 61. Thearrangement is such that the links 65, 66 maintain the -bogle in properrelative position in a fore and aft direction, yet enable the bogle torise or fall relatively of the cross-brace 3|, and to tilt angularlyabout the shaft 64 for a purpose presently to be explained. It will beobserved that the links 65 and 66 extend somewhat upwardly from theshaft 64 to shaft 61 and axle 53, and are at an angle to each other soas to act as a toggle against the arms 45 and 52 when the bogle is movedup or down with relation to the side rails 30.

The bogle is disposed directly below the crossbra'ce 3l, and positionedbetween the latter and the top plate 60 of the bogle and secured .toeach of them is a pneumatic spring element comprising a bellows-shapedstructure 10. The structure is centrally disposed with relation to thesides of the landing gear and is composed of flexible, imperviousmaterial. It is preferably formed with a medial circumferential reducedor constricted region, which region is encircled by an inextensiblemetal girdle ring 1|. Valve 12 is provided for inating the bellowsstructure with compressible fluid such as air, the air within thebellows being maintained at sufcient pressure to enable the bogie tosupport its proper proportionate share of the load on the landing gear.The arrangement provides ready means by which the landing gear may beadjusted to support loads of various weights. Furthermore, the inflatedbellows urges the bogle toward the lower reach of the endless track S4and maintains the latter taut when there is no load on the landing gear.

During flight each landing unit A is carried within closed nacelle Il ofthe airplane i0, but preparatory to landing is lowered to the positionshown in Fig. 6. It will be observed that the shock-absorbing element 26is in extended condition and holds the undercarriage structureconsisting of the arms 20, 22 and 25 in somewhat open position,Furthermore, the compression 6 is reduced. In Fig. 4 the position of thetrack structure in lo'adedmosition on level ground is shown in fulllines, the relative positions of the various elements in unloadedcondition, -as in flight, being indicated in broken lines.

The major portion of landing impact is absorbed in the shock absorber 26as the arms 20, 22 and 2i move from the positions shown in Fig. 6 to thepositions `shown in Figs. 'I and 8. A minor, but appreciable portion ofthe impact is absorbeddn the track portion of the landing gear,especially by the endless band track itself. It will be apparent thatthe impact of landing will result in the swinging of the arms and 52rearwardly. This would result in a slackening the force absorbed by thedeforming of the pneumatic cushion 10 in cushioning the landing impact.The feature of automatically imparting additional tension to the endlesstrack upon landing lalso is advantageousl in that it counteractscentrifugal force in the track as it is driven rapidly over the ground.It is also advantageous in keeping the track in tight -frictionalengagement with the drums 4| and 54 so that braking force applied to thelatter will be efficiently transmitted to the track.

Since the weight of the airplane is applied to the side rails 30 of thelanding gear at 32,

forwardly of the rear axle 53, the nose or leading end of the gear movesdownwardly against the force of the springs in cylinders 35, so that thelower reach of the track is in contact with the ground even over a largearea. The action is shown in Fig. 4, where the freely suspended positionof the track unit is shown in dotted lines and the loaded position infull lines.

The arrangement by which the bogle may swivel or tilt about the shaft 64is especially advantageous when moving over rough ground, as shown inFig. 8, since it enables both bogle wheels to maintain normal engagementwith the endless track and prevents undue slackening of the tension inthe latter. Moreover, the use of a deformable pneumatic spring membersuch as the ward. pressure to be exerted on the bogle at all Y times,notwithstanding the Various angular springs in the cylinders 35 hold theentire track over, due to the striking of small obstructions,

positions the latter may assume.. The forward roller 41 will yield ingoing over obstructions, its upward movement being resisted by thecushion ill through the toggle mechanism, The spring 48 acts as abalance for the cushion 10. The drum' 54 also has the ability to yield.As the several rollers 41, 63 and 54 have considerable freedom ofmovement, the device will accommodate itself to all manner of rough anduneven ground.

The trackv44 as illustrated in detail in Fig. 10 has a thin, ilexible,molded rubber body structure 13, a frictional inner facing of rubberizedfabric 14, a tread'15 of tough, abrasion-resistant rubber compound, anda reinforcing structure of flexible stranded steel 4wires 16 embedded inthe gum plies 11, the whole being vulcanized in annular form as anintegral body. The wires are small flexible .cables placed closelytogether.

These cables, which are spaced approximately 14 to the inch, are made upof a plurality of strands of very fine wire, the complete cable beingapproximately .030" in diameter. The cables which have been found togive the bestI results are made of what is known as fine tire wire withthe specifications as 'U3/.0058. As a result the wire reinforcement isvery flexible so that it will not cut through the belt. A belt soconstructed will withstand the high speeds-to which the track issubjected on landing. Y

Because the endless tracks 44 having a much greater area of contact withthe ground than have the pneumatic tires such as usually are ernployedon landing gear, it follows that the brakgreater mechanical advantagethan braking applied to wheels equipped with pneumatic tires.

Thus, airplanes equipped with the improved land- .area of the track,with the result that the possibility of nosing over upon landing isfurther reduced.

It will also be noted that the arrangement is such that the track andits reticulated supporting structure will conform to the surface of theterrain more effectively and safely than previous landing gears of thisgeneral type. Thus, in llg.

7 is shown the position which the track unit assumes when the groundslopes downwardly and forwardly, while Fig. 8 shows the position whichis assumed on an upwardly sloping terrain or in going over obstructions.The fact that the forward drum Il is elevated above the contact area ofthe track enables the device to climb over obstacles. The superiorflexibility of the structure which absorbs the irregularities of alltypes of rough ground greatly reduces any tendency of the plane to upsetor nose over during landing or taking off on very rough and unevenground. This is all accomplished without danger of the structurethrowing its landing track, as is -often the case with previous landinggears of this type.

It will be understood that the means shown for spreading the main trackcarrying drums may be altered, it being possible to employ other meansresponsive to the load for spreading the drums under load or to take upany loosening of the belt by centrifugal force while under load.

While the specifications of the wire reinforcement given above have beenfound to be highly satisfactory and eillcient, it will be understoodthat these details may be modified, it being-essential to maintain avery flexible construction which will, however, have the requisitestrength. It will also be noted that by the provision of a plurality ofribs of equal size and spacing,the belt may shift on the rolls andpulleys ,to a considerable extent without actual loss ofthe belt as anyrib will seat properly within any groove and the belt still beserviceable.

' ing effort of the present invention will have A Other modificationsmay be resorted to without departing from the spirit of the invention orthe scope thereof asdeflned by the appended claims.

What is claimed is:

1. An -endless band track of the class described comprising a pliablerubber-like.- body portion having numerous'parallel, longitudinallyextending, radially inwardly projecting. endless ribs on the-entireinner face of the track, said ribs defining grooves therebetween,said'ribs and grooves having a facing of rubberizedfabric, vulcanizedthereto said body being reinforced across a major portion of its entirewidth with at least two layers of closely spaced small wire cables, saidcables being made up of a plurality of strands of flne wire.

2. 4An endless band track ofthe class described comprising a soft rubberbody portion having numerousi parallel, substantiallyidentical,longitudinally extending, radially inwardly projecting, endless ribs onsubstantially they entire width of the track, said ribs defining groovestherebetween,

' said ribs and grooves having a facing of rubberized fabric, said bodybeing reinforced across substantially its entire width with atleast twolayers of closely spaced small wire cables, said cables being made up ofa plurality of strands of wire, said cables being disposed in said bodya substantial distance radially dutwardly from the base of said ribs.

3.. An endless track of thecharacter described comprising a ribbon-likeendless body portion of deformable material, a reinforcing elementconsisting of a flexible metallic multiple strand cable imbedded withinsaid body portion and disposed in multiple convolutlons to define areinforcing layer between the outer and inner wall surfaces of said bodyportion, said reinforcing layer ex.

tending laterally across a major portion of said body portion, said bodyportion being provided with a multiplicity of longitudinally extendingintegral ribs projecting radially inwardly from the inner surfacethereof, and spaced to define grooves therebetween.

RAYMOND W. ALLEN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

